feat(vm): reducing USB device downtime during VM migration

[yaroslavborbat]

Description

This PR improves USB device migration for virtual machines by delegating USB migration logic to KubeVirt.

Changes:

• Removed all USB device detach/attach logic around migration from virtualization-controller
• Migrated USB migration handling to KubeVirt fork: feat: add usb migration strategy annotation 3p-kubevirt#77
• Introduced USBMigrationStrategyAnn annotation on KVVMI to control USB device behavior during migration
• Default strategy is USBMigrationStrategyIgnore: USB device is not detached before migration, instead it is ignored on the target domain and automatically detached/re-attached when the VM switches to the target node

Why do we need it, and what problem does it solve?

Previously, the USB migration logic was implemented in virtualization-controller:

1. USB device was detached from the VM before migration started
2. VM migrated to the target node
3. USB device was attached again after migration completed

This approach caused significant downtime for USB devices during migration — the device was unavailable from the detach operation until the attach operation completed on the target node.

The new approach moves this logic into KubeVirt and uses the USBMigrationStrategyAnn annotation (set to USBMigrationStrategyIgnore) on the KVVMI object:

• USB device is not detached before migration
• On the target node, USB device is initially ignored (not attached during migration)
• When the VM switches to the target node, the USB device is automatically detached from source and re-attached on target
• This significantly reduces USB device downtime

What is the expected result?

1. Create a VM with an attached USB device
2. Initiate live migration of the VM
3. Verify that USB device downtime is minimal (detach/re-attach happens atomically when VM becomes active on target)
4. After migration completes, verify that USB device is successfully attached on the target node
5. VM migration completes successfully

Expected behavior:

• USB device downtime is reduced from "full migration duration + detach/attach overhead" to near-instant detach/re-attach
• USB device is automatically re-attached on the target node after migration
• No USB-related migration logic remains in virtualization-controller
• USB migration behavior is controlled by the USBMigrationStrategyAnn annotation on KVVMI

Checklist

• The code is covered by unit tests.
• e2e tests passed.
• Documentation updated according to the changes.
• Changes were tested in the Kubernetes cluster manually.

Changelog entries

section: vm
type: feature
summary: Reduced USB device downtime during virtual machine migration.

[prismagod]

Do we need to update this alert in USER_GUIDE.md?

Upd: updated the alert in the 1.7.0 documentation PR.